Chapter 8. Chapter 8: Community Ecology

Interactive Study Guide

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Guiding Question 8.2

How do biotic and abiotic factors affect community composition, structure, and function?

Why You Should Care

Understanding the interplay of biotic and abiotic factors is essential for maintaining healthy communities and functioning ecosystems, which is very important for humans. The Chesapeake Bay is a good example (see Chapter 16): According to accounts from early European explorers, the Chesapeake Bay was startlingly clear all the way to the sandy bottom. Nowadays, the water is always cloudy and opaque. Why the difference? Over the centuries, the seemingly bottomless supply of oysters in the Bay finally bottomed out when overharvesting slowly destroyed the industry in the 1900s. Oysters feed by filtering organic matter and microorganisms out of water, so with the oysters gone, there was no one to filter the water. This, in turn, contributed to the die-off of most of the eelgrass (a submerged aquatic plant) in the shallow portions of the bay because eelgrass needs clear water to get enough sunlight to grow. Eelgrass provides habitat for juvenile crabs and fish, so losing it hurt those industries as well. Abiotic and biotic factors affecting communities isn’t just a vague notion about an idealized ecosystem; it’s something that can hit close to your home and table.

Test Your Vocabulary

Choose the correct term for each of the following definitions:

Term	Definition
	The relative abundance of each species in a community.
	The total number of different species in a community.
	The role a species plays in its community, including things like how it gets its energy and nutrients, what habitat requirements it has, and which other species and parts of the ecosystem it interacts with.
	Species that prefer core areas of a habitat—areas deep within the habitat, away from the edge.
	The ability of an ecosystem to recover when it is damaged or perturbed.
	Regions of distinctly different physical areas that serve as boundaries between different communities.
	The different physical makeup of the ecotone, which creates different conditions that either attract or repel certain species (for instance, it is drier, warmer, and more open at the edge of a forest and field than it is further in the forest).
	The physical environment in which individuals of a particular species can be found.
	The variety of species in an area; includes measures of species richness and evenness.
	Species that prefer to live close to the edges of two different habitats (ecotone areas).

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5.

Infographic 8.3: Measuring Species Diversity

Thought Question: What can you infer about habitat types and human population density in the lower and upper halves of Florida based on the information in the map?

The description of this map explains that lower bird diversity is associated with human development and homogenous habitats like agricultural fields and tree plantations. Since diversity is lower in the lower half of the state, you could assume that habitats are more homogenous and developed for human use in south Florida.

The interior of a mature forest is usually fairly open because the shade of the trees prevents dense vegetation from growing there. The border between a forest and a field, however, often has thickets of shrubs or vines that thrive in the extra light.

6.

Where in the forest diagram above would represent an ecotone?

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